A silver halide color photographic material has, in general, silver halide emulsion layers each having a sensitivity to each of three primary colors of blue, green and red, and each emulsion layer colors in yellow, magenta or cyan, individually, to reproduce a color image, by means of a so-called subtractive color process.
Accordingly, a color image to be reproduced is influenced by the wavelength range to which each photographic layer is sensitive (that is, spectral sensitivity distribution), and in addition, said color image largely depends upon the hue of yellow, magenta or cyan to be colored in each layer, or that is, the spectral absorption characteristic of the coloring dye. In general, said characteristic is not sufficient enough to satisfy a theoretical and ideal color photographic system because of various limitations on the materials to be used. Regarding a coloring dye of a coupler which is generally used as a coloring material in a silver halide color photographic material, for example, some have a spectral absorption in wavelength range, or some others have a second absorption maximum in visible wavelength range, and therefore are not always ideal coloring materials to be used as three primary colors in a subtractive color process.
Under the circumstances, color images obtained in conventional silver halide color photographic materials are not considered to be able to sufficiently reproduce all colors of an object, and the saturation and the hue of the formed color images often somewhat differ from those of the corresponding object.
In order to overcome such inconvenience that the color of an image and that of an object differ in the saturation and the hue, various efforts have heretofore been made in this technical field, for example, to improve the spectral sensitivity distribution of a photographic material or to improve the spectral absorption characteristic of a coloring dye.
One means for improving the spectral absorption of a coloring dye to obtain a sharp spectral absorption with less side absorption is to develop a novel coupler constitution. For instance, development of pivaloyl type yellow couplers (as described in U.S. Pat. No. 3,408,194), anilino type magenta couplers (as described in Japanese Patent Application (OPI) Nos. 74027/74 and 111631/74) (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") and pyrazolotriazole type magenta couplers (as described in U.S. Pat. No. 3,725,067) intends to attain said improvement.
Another means is to change the existing state of a coloring dye in a photographic emulsion of a photographic material so as to improve the spectral absorption of said coloring dye.
For instance, the selection of a high boiling, coupler dispersing solvent is one means for changing the existing state of a coloring dye. Also, U.S. Pat. No. 3,676,137 describes the use of a pyrazolone magenta coupler and a phosphate ester of a high boiling solvent so as to shift the absorption of the coloring dye to the side of a short wavelength range whereby any excess absorption of red rays may be reduced. In addition, phenol compounds which are described in U.S. Pat. No. 2,835,579 as having a high boiling point generally have a high polarity. Journal of the American Chemical Society, 73, 919 (1951), etc., report that a pyrazolone-azomethine dye and a phenol type compound may form a hydrogen bond whereby the spectral absorption of the pyrazolone-azomethine dye may be shifted to the side of a long wavelength range. Regarding the use of phenol compounds as a high boiling solvent, U.S. Pat. No. 4,178,183 describes a technique for formation of an infrared ray absorption zone to be used as a recording zone for a color cinematograph movie by the use of a cyan coupler and a phenol type high boiling solvent; and Japanese Patent Application (OPI) No. 171953/84, etc., describe that the spectral absorption characteristic of a 2,5-diacylaminophenol type cyan coupler varies according to the used phenol type high boiling solvent. Said techniques result from the utilization of the fact that the spectral absorption of a cyan dye may be shifted to the side of a long wavelength range by the use of a phenol type high boiling solvent.
None of the above described prior art techniques, however, could attain a sufficient improvement of color reproducibility in silver halide color photographic materials, which is aimed at by the present invention.
A so-called interlayer effect has been developed, where color purity is elevated by means of a development effect, as described in Belgian Patent No. 710,344 (corresponding to U.S. Pat. No. 3,536,487) and German Patent No. 2,043,934 (corresponding to U.S. Pat. No. 3,713,828); and a so-called DIR coupler (as described in U.S. Pat. No. 3,227,554) has been developed for the application of said technique to the field of color photography.
In addition, some other various proposals have heretofore been made in this technical field, including a method where any unnecessary absorption effect of a coloring dye is corrected by the use of a colored coupler having a self-masking function (as described in U.S. Pat. No. 2,455,170) or a method where the spectral sensitivity of each light-sensitive layer is sharpened so as to improve the color separation, etc.
However, any of said methods could not also attain a sufficient color reproducibility as yet.
Apart from said prior art methods, another method has been tried, where plural couplers each forming a coloring dye of a different spectral absorption are used in one emulsion layer.
For instance, a method where a small amount of a different kind of an additional coupler is added to a main coupler whereby "color mixture of an image" is forced is described in Japanese Patent Publication No. 391/65, and a method where two or more magenta couplers are co-used thereby to partially improve the insufficiency of the absorption characteristic of a color image obtained from a main coupler is described in Japanese Patent Application (OPI) No. 71333/75 (corresponding to British Patent No. 1,488,855).
However, said methods still are defective in that the color density range of color reproducibility is narrow.
Under the circumstances, another proposal has been made for a method of formation of a color image with a good color reproducibility from a low density to a high density, saying that it is preferred to change the maximum absorption wavelength of three primary color dyes of a subtractive color process in a high density part and in a low density part, on the basis of a color technological theory. (Said proposal is described in The Color Gamut Obtainable by the Combination of Subtractive Color Dyes (Photo. Science and Engineering), Vol. 15 (5), pp. 399-415 (in 1971).)
Japanese Patent Publication No. 43887/74 (corresponding to U.S. Pat. No. 3,811,890) describes a method for improving a color reproducibility of a color image by utilizing said theory.
In said method, a silver halide color photographic material having three silver halide emulsion layers each having a sensitivity to each of three primary colors of blue, green and red is used and each of said light-sensitive layers contains two or more couplers each having a different coloring maximum absorption wavelength by 5 nm or more and each having a different coupling speed, whereby the color reproducible density range may be broadened.
Said method is, however, practically difficult and defective in that usable couplers are limited in view of the synthesis thereof or of any other various characteristics thereof (such as solubility, color stain) than the coloring characteristic thereof and that the gradation is apt to vary and the hue is apt to slip off due to the difference of the processing technique in the development step since plural couplers each having a different coupling speed are used.
In particular, the reduction of a colored density is remarkably large because of the reduction of the stirring of a processing bath during development, which is an extreme problem in practice.